1. Field of the Invention
The present invention relates to sewing machines, and more particularly to a needle-changing mechanism for use in multiple-needle embroidery sewing machines.
2. Description of Prior Art
The sewing of embroidery on fabrics is often carried out using multiple needles. Each of these needles bears a thread of a different color such that the embroidery can be made with various colors. In the operation of sewing machines, applying a different color to the embroidery requires simply the changing of the current working needle to another one that bears the thread of the desired color.
FIG. 1 shows one prior art needle-changing mechanism for use in embroidery sewing machines, which was developed by TAJIMA Company of Japan. The needle-changing mechanism includes a sewing head 11, a set of sewing needles 12, a transmission bar 13, a sliding block 14, a sliding column 15, a motor 16, gear sets 17, 17', a spiral shaft 18, a circuit board 19, a large disk 110, a small disk 111, a photo detector 112, an output signal line 113 coupled to the large disk, and an output signal line 114 coupled to the small disk. The sliding column 15 can be driven to move by the spiral shaft 18. When the motor 16 rotates, it drives the spiral shaft 18 via the gear set 17, thereby moving the sliding block to slide horizontally to the left or to the right, which in turn moves the sewing needle 12 on the sewing head 11 to move accordingly to change the working needle to another.
When the spiral shaft 18 rotates, it in turn drives the large disk 110 and the small disk 111 via the gear set 17'. A number of proximity detectors equal to the number of sewing needles are provided on the large disk 110. During a needle-changing process, when the desired needle, say needle #1, is about to reach the working position, a proximity detector on the large disk, say the proximity detector #1, reaches Position A, thereby generating a first positioning signal. On the small disk 111, there are two gap portions, which are operatively related to the photo detectors 112. When the desired needle #1 reaches the working position, one gap portion lies within the space between the two side walls of the photo detector 112, thereby allowing the light beam to pass therethrough, which generates the second positioning signal. The action of the whole needle-changing process is based on these two positioning signals.
It is a drawback of the foregoing prior art that two positioning signals have to be used for the needle-changing action. Moreover, the prior art devices lack the capability to restore the position of current working needle after a power failure which would cause the working needle to be out of position. Furthermore, since gear sets 17 and 17' are used, the cost and complexity in assemblage are greatly increased.
FIG. 2 shows another prior art needle-changing mechanism, which was developed by HAPPY Company of Japan. This prior art uses a plurality of photo detectors in cooperation with a disk without gap portions. The structure includes a sewing head 21, a set of sewing needles 22, a transmission bar 23, a screw 24, sliding columns 25a-25c, a motor 26, a gear set 27, a spiral shaft 28, a circuit board 29, an array of photo detectors 210, a small disk 211, a photo detector 212, an output signal line 213 coupled to the photo detectors, an output signal line 214 coupled to the small disk 211, and a sensing plate 215. The array of photo detectors 210a-210e are arranged along a straight line on the circuit board and the photo detector 212 is arranged in another position. The sensing plate 215 is not provided with any gap portions and is fixed to the transmission bar 23 by means of the screw 24. In operation, the sensing plate moves through the gaps of the photo detectors 210a-210e. The sliding column 25a is inserted in the grooves of the spiral shaft 28 and the sliding column 25b-25c are directed into the grooves one after the other when the spiral shaft 28 moves.
When the motor 26 rotates, the spiral shaft 28 is driven to move the transmission bar 23 horizontally to the left or to the right, thereby carrying out the needle-changing process. Taking the drawing of FIG. 2 as an example, when the sensing plate 215 blocks the light beam in the photo detector 210c and not in the photo detectors 210b and 210d, a signal pattern (210a, 210b, 210c, 210d, 210e)=(0,0,1,0,0) is generated from the circuit board.
During the needle-changing process, when the desired needle, say the needle #4, reaches the working position, the sensing plate will block the light beam in the photo detector 210d, thereby causing the generation of a signal pattern (210a, 210b, 210c, 210d, 210e)=(0,0,0,1,0), which is termed the first positioning signal. This also actuates the driving of the small disk 211. When the desired needle #4 reaches the working position, the gap portion on the small disk 211 lies within the space in the photo detector 212, which is equivalent to the photo detector 112 of the first prior art, thereby allowing the light beam to pass through the gap portion on the small disk 211 and thus causing the generation of the second positioning signal. The action of the whole needle-changing process is based on these two positioning signals. It is a drawback of this prior art that its structure includes the gear set 27 and the small disk 211, which significantly increase the cost in mechanical parts and assemblage. Moreover, the requirement of two positioning signals increases the complexity of the structure. It also lacks the capability to restore the position of the current working needle after a power failure which would cause the working needle to be out of position.